Oscillating signal playback circuit
The present invention relates to the playback circuitry of the swinging signal that writes down on the recordable disc of CD.
At present, except that such as the read-only optical discs such as CD or DVD-RAM, all put on market such as Write once optical discs such as CD-R/DVD-R with such as CD-R such as CD-RW/DVD-RW or DVD-RAM.Record can't carry out during CD-R in conventional read-only disk, carry out generate the clock signal with replay signal.Therefore, as the groove of disc recording message part with constant periodic oscillations, the clock signal the when swinging signal that obtains from this swing of resetting by the push-pull type system (swing hereinafter referred to as) generates record.
Fig. 2 has shown the conventional example of oscillating signal playback circuit.On photodetector 1 in two, form far-field pattern 2 from the reflected light that shines the laser spots on the dish.Two output signals of photodetector are carried out subtraction by subtraction circuit 17 and are obtained and recommend component.From the push-pull signal that obtains, extract hunting frequency by bandpass filter (BPF) 18.The swinging signal of resetting from CD-R/RW is that frequency is the continuous signal of 22.05KHz ± 1KHz.In CD-R/RW, be superimposed upon on this swinging signal by the FM modulation owing to be called the address information of ATIP (absolute time in Absolute Time In Pregroove-pre-groove), so it has a certain frequency span.Fig. 3 is the view of the panel surface of a DVD-R/RW.Label 301 in the accompanying drawing is represented record data and is similar to the groove that CD-R/RW swings.The swinging signal of resetting among the DVD-R/RW is that the frequency that is different from CD-R/RW is the continuous signal of 140.65KHz, and the address information that do not superpose.In addition, the holes that are called plane pre-pits between groove (LPP hereinafter referred to as) of 302 expressions are recorded in surface portion between the groove of recorded information between the groove and not.LPP is positioned at from the zone of the most preceding three maximum amplitude positions, maximum amplitude position to the of certain swing, and address information writes down by these three positions.
In order stably from push-pull signal, to extract swinging signal, be necessary to reduce the RF signal that bleeds in the push-pull signal.Therefore, disclosed in the flat 8-194969 of the announcement of Japanese patent unexamined, might an automatic gain control circuit (agc circuit) be set in the prime of the subtraction circuit of Fig. 2.
In addition, in recent years, along with the increase of dish capacity, the technology that doubles raising dish playback speed is developed rapidly.
In the twice speed playback, be necessary to change the passband of the swing BPF relevant with twice speed.As the method that causes this relation, though being playback speed according to dish, setting that might the BPF passband changes, because each this speed that changes all needs to visit microcomputer, so this processing bothers by microcomputer.Carrying out by increase dish playback speed under the situation that CAV resets, because the skew that the BPF passband is provided with appears in the number of times of limiting access microcomputer, the factor that this signal to noise ratio (S/N ratio) that becomes swinging signal descends, and therefore make the clock jitter increase.About this problem, disclosed in the flat 11-203681 of the announcement of Japanese patent unexamined, might use the passband of finishing by pseudo filter (dummy filter) and phase-comparison circuit from motion tracking.
As mentioned above, under the situation of the twice speed playback of realizing various dishes by a disc reproducing apparatus, because variety of issue can take place the specification difference of each dish.The problem of oscillating signal playback circuit has following several:
1.DVD-R/RW groove between surperficial pre-pits signal bleed in the swinging signal
Herein, in the flat 8-194969 of the announcement that resembles Japanese patent unexamined disclosed and be provided with under the situation of agc circuit in the prime of the subtraction circuit of Fig. 2, in playback of DVD-R/RW, the LPP signal bleeds in the RF signal, and AGC (automatic gain control) gain is that the variation according to amplitude changes.Therefore have a kind of worry, by LPP the time, the RF signal can bleed in the swinging signal.
2. to there not being the processing of swinging signal in the DVD-RAM address information district.
Fig. 4 is the view of DVD-RAM panel surface.Label 403 expression grooves in the accompanying drawing; Surface between 404 expression grooves.In order to increase the density of record, DVD-RAM adopts surface groove register system between groove, and wherein signal not only is recorded in groove 403 but also be recorded in surface 404 between groove.Therefore, about the surface and the rail of record separately of groove between the grooves of 401 and 402 expressions in the accompanying drawing, write down address information among the DVD-RAM in the mode of interlocking.The part of recording address information is called PID (physical label data) district.
Though being similar to DVD-R/RW, the swinging signal of resetting among the DVD-RAM has single-frequency 157KHz like that, but because this address information is recorded in the PID district with interlace mode, so recommend component and when it is deducted, before subtraction, at one end do not have signal when detecting.Therefore, with above-mentioned first the same, consider that the prime at subtraction circuit is provided with under the situation of AGC (automatic gain control) circuit, might AGC (automatic gain control) saturated in the PID district.
In addition, the swinging signal of resetting among the CD-R/RW has a certain bandwidth, and amplitude changes.In order to reduce the side-play amount that causes by in the level binaryzation process of back, disclosed in the flat 11-161961 of the announcement of Japanese patent unexamined, might AGC (automatic gain control) circuit be set in the back level of BPF 18., in DVD-RAM,, thereby when playback PID district, there is not swinging signal because groove is or not the PD district.Therefore, same as above, might this AGC (automatic gain control) circuit saturated in the PID district.
3.BPF passband setting
In the flat 11-203681 of the announcement of Japanese patent unexamined, in the disclosed technology, there is the accuracy problem that the swinging signal band detects in pseudo filter and the phase-comparison circuit, and the problem that increases circuit scale for the degree of accuracy that improves circuit.Under situation about being provided with according to the passband that is carried out BPF by the clock signal of oscillating signal playback, debatablely be: the swinging signal frequency is different according to the kind of CD with the ratio of clock frequency.
Like this, because the specification of swinging signal is different according to dish, thus there is a problem, under the situation of setting corresponding to the oscillating signal playback circuit of various dishes, the corresponding increase of circuit erection space.
In order to address the above problem, at the oscillating signal playback circuit that is used for resetting to by the swinging signal that makes the groove that forms on the dish have swing to write down, this oscillating signal playback circuit comprises the computing circuit that is used to calculate push-pull signal, from the output signal of described computing circuit, extract the bandpass filter that the hunting frequency component is used, be arranged on computing circuit prime or inner AGC (automatic gain control) circuit, and pre-pits pick-up unit in plane between groove, the latter is used to detect and is in plane preset pit area between the groove that forms the hole on the surface portion between the groove of recorded information between the groove and not, and have such structure: AGC (automatic gain control) circuit and fix, perhaps the detection signal of plane pre-pits pick-up unit changes between the response time constant of plane preset pit area playback time AGC (automatic gain control) circuit between groove is by groove.
In addition, also has address information recording district pick-up unit, be used to detect the address information recording district, wherein write down planar section calculated address between the divided groove of rail at groove, also have the gain of so a kind of structure: AGC (automatic gain control) circuit to fix, or the response time constant of AGC (automatic gain control) circuit is then changed when playback address information recording district by the detection signal of address information recording district pick-up unit.
Moreover, also has the 2nd AGC (automatic gain control) circuit at the output terminal that is used for extracting the bandpass filter of swinging signal from push-pull signal, also have a kind of like this structure: the gain of this AGC (automatic gain control) circuit and the 2nd AGC (automatic gain control) circuit is all fixed, and perhaps the response time constant of this AGC (automatic gain control) circuit and the 2nd AGC (automatic gain control) circuit all is converted when playback address information recording district.
In addition, also be useful on and detect the device treat cut and finger mark on the playback dish, and a kind of like this structure: the gain of this AGC (automatic gain control) circuit is fixed, and perhaps the response time constant of this AGC (automatic gain control) circuit changes according to the exclusive disjunction output signal of the detection signal of plane pre-pits pick-up unit between this Device Testing signal and groove.
Moreover, also have a kind of like this structure: the gain of this AGC (automatic gain control) circuit and the 2nd AGC (automatic gain control) circuit is all fixed, and perhaps the response time constant of this AGC (automatic gain control) circuit and the 2nd AGC (automatic gain control) circuit all changes according to detection wait the to reset exclusive disjunction output signal of detection signal of the Device Testing signal of the cut of CD and finger mark and address information recording district pick-up unit.
In addition, between groove plane pre-pits pick-up unit according to the signal that produces corresponding to the detection signal of preset pit area position in plane between groove or from this Device Testing signal and and the clock that obtains synchronously of CD speed detect pre-pits recording areas in plane between groove.
Moreover, the signal that address information recording district pick-up unit produces by the signal that produces corresponding to the detection information of address information recording zone position, from this detection signal and swinging signal or from this Device Testing signal and detect the address information recording district with clock that CD speed obtains synchronously.
In addition, the passband of bandpass filter is directly proportional with the clock frequency that CD speed obtains synchronously substantially, and the scale-up factor between passband and this clock frequency can be changed.Moreover, also be useful on the cut of detection dish or the scratch detection circuit of finger mark, and a kind of function that is used for the passband of fixed band bandpass filter when detecting cut.
In addition, also have a kind of function, wherein measure the clock frequency that obtains with the dish synchronization, and when frequency variation is big described in the normal playback process, the passband of bandpass filter is fixed.
In addition, the computing circuit that is used to calculate push-pull signal has the passband that plane pre-pits signal passes through between the groove that allows plane preset pit area between groove, and pre-pits pick-up unit in plane between groove is provided, be used to make the output signal of computing circuit to become pre-pits signal in plane between groove.
Moreover, oscillating signal playback circuit comprises, be used to calculate the computing circuit of push-pull signal, be used for extracting the bandpass filter of swinging signal frequency component from the output signal of computing circuit, and the subtraction circuit that is used for deducting from the output signal of computing circuit the output signal of bandpass filter; Also have a kind of like this structure: computing circuit and subtraction circuit have the passband that plane pre-pits signal passes through between the groove that allows plane preset pit area between groove; And also have plane pre-pits pick-up unit between groove, be used for the output signal of subtraction circuit is handled plane pre-pits signal between grooving.
Fig. 1 is the circuit block diagram of the oscillating signal playback circuit of first embodiment of the invention.
Fig. 2 is the circuit block diagram of conventional oscillating signal playback circuit.
Fig. 3 is the synoptic diagram of plane pre-pits between the groove of DVD-R/RW.
Fig. 4 is the synoptic diagram in the PID district of DVD-RAM.
Fig. 5 is the circuit block diagram of example of AGC (automatic gain control) circuit of first embodiment of the invention.
Fig. 6 is pre-pits signal the bleed synoptic diagram of RF signal in plane between playback of DVD-R/RW time slot.
Fig. 7 is the circuit block diagram of example of the band pass filter circuit of first embodiment of the invention.
Fig. 8 is the circuit block diagram of example of the band pass filter circuit of second embodiment of the invention.
Fig. 9 is the circuit block diagram of example of AGC (automatic gain control) circuit of second embodiment of the invention.
Figure 10 is the circuit block diagram of example of the band pass filter circuit of second embodiment of the invention.
Figure 11 is the input clock frequency of current source 905 of wave filter of Figure 10 and the view of the relation between the output current.
Figure 12 is the circuit block diagram of the oscillating signal playback circuit of third embodiment of the invention.
Will be before the explanation accompanying drawing used label in the description of the drawings.
1,3 ... photodetector, 2 ... far-field pattern, 111,112,1101 ... adding circuit (SUM), 113,114 ... high bandpass filter (HPF), 21 to 23 ... AGC (automatic gain control) circuit, 28,117 ... subtraction circuit, 20 ... microcomputer, 23 ... bandpass filter (BPF), 25 ... binarization circuit, 26 ... phase lock ring (PLL) circuit, 27 ... pre-pits testing circuit in plane between groove, 301,403,701 ... the recorded in wobbles rail, 302 ... plane pre-pits between groove, 401,402 ... the PID part, 502 ... amplitude detection circuit (DET), 504 ... charge pump circuit (CP), 601 to 603 ... operational amplifier, 901,902 ... the gm variable amplifier, 905 ... variable current source, 908 ... the fixed current source, 1102 ... the scratch detection circuit, 1104 ... or circuit.
Fig. 1 is the circuit block diagram of first embodiment of the invention.In the figure, have with Fig. 2 in the unit of unit identical function use with Fig. 2 in identical character represent that and its explanation is omitted. Label 111 and 112 expression broadband adding circuits; 113 and 114 expression broadband HPF; 117 expression broadband subtraction circuits.Label 21,22 and 24 expressions have AGC (automatic gain control) circuit that gain keeps function, and gain is by fixing from the control signal of microcomputer 20.Wherein, AGC (automatic gain control) circuit 21 and 22 that is positioned at the prime of recommending computing circuit that is made of subtraction circuit 117 is set to wideband A GC (automatic gain control) circuit.But, HPF 113 and 114 and subtraction circuit 117 be defined as recommending under the situation of computing circuit, though all becoming, these circuit are arranged on AGC (automatic gain control) circuit of recommending in the computing circuit, but, present embodiment recommend the part that computing circuit refers to subtraction, and hereinafter, AGC (automatic gain control) circuit 21 and 22 all is arranged on the prime of recommending computing circuit.Label 27 expressions are used for the circuit of detection record at the LPP of DVD-R/RW signal, by making these circuit from the adding circuit to the subtraction circuit have the detection that the broadband just may be finished LPP by circuit structure.The basic BPF that changes with clock frequency of label 23 expression passbands with being directly proportional, and the scale-up factor between clock frequency and the passband can change by microcomputer 20.Label 25 expressions are with the amplitude limiter circuit of swinging signal binaryzation.Label 26 expression is used for generating from the swinging signal of binaryzation the PLL circuit of clock signal.Label 1101 and 1102 expressions are used for detecting from the RF signal defect detection circuit of the cut, finger mark etc. of dish.Label 101 expressions are to the control signal of AGC (automatic gain control) circuit; 102 expressions are to the control signal of BPF 23.
Fig. 5 illustrates the example of the circuit structure of AGC (automatic gain control) circuit 21,22 or 23.Label 501 expressions in the accompanying drawing are used for carrying out by voltage V0 the gain variable amplifier (AMP) of gain control; 502 expression testing circuits, latter's detected amplitude and output are poor as control voltage with reference voltage VR's.Label 504 uses to come electric capacity 506 is discharged and recharged from the control voltage output signal of waveform detection circuit 502.Label 505 expression AGC (automatic gain control) maintained switchs, when this switch disconnected, the control voltage V0 of gain variable amplifier 501 is kept by electric capacity 506 and the gain of amplifier 501 is fixed.
Hereinafter, the AGC (automatic gain control) with the explanation present embodiment operates.
When playback CD-R/RW, swing is a continuous signal, and there is not the hole in surface portion between groove, so seepage can not take place.Therefore, the switch 505 of Fig. 5 is positioned at on-state all the time, and does not keep AGC (automatic gain control) operation.
The output waveform synoptic diagram of photodetector when Fig. 6 is a playback of DVD-R/RW.
In by swing 701 on the luminous point 702 playback dishes during signal of record, the amplitude of the output signal 703 of photodetector changes resembling shown in 704 because of the seepage of signal due to the LPP among Fig. 1.Therefore, when playback LPP, the switch 505 of Fig. 5 disconnects, so that recommend AGC (automatic gain control) operation of the AGC (automatic gain control) 1 and 2 of computing circuit prime among maintenance Fig. 1, and the amplitude change is not followed in the gain of AGC (automatic gain control) 1 and 2.Because the swing of the groove of LPP and dish synchronously, so LPP testing circuit 27 detects after first LPP in the accompanying drawing, to counting the position of detecting this LPP, and keep AGC (automatic gain control) to operate by microcomputer by the clock signal of oscillating signal playback.Like this, because of the RF amplitude changes AGC (automatic gain control) change in gain caused, and can reduce the RF signal and bleed in the swinging signal when having prevented playback LPP.Moreover, except that the above, operation for the AGC (automatic gain control) 3 of level behind the BPF among Fig. 1, by carry out with at the identical control of AGC (automatic gain control) 1 and 2, the variation that the AGC (automatic gain control) 3 that is caused by the change of swinging signal amplitude in the time of might preventing to reset LPP gains and the playback of stable oscillation signal.
As shown in Figure 4, in DVD-RAM, because data are to be recorded in PID district 401 and 402 with interlace mode, under the situation of the swinging signal in these districts of resetting by the circuit of Fig. 1, exist the input end of AGC (automatic gain control) 1 and 2 not have signal and the saturated possibility of operation.In addition, because there is not groove in the PID district, so exist in the saturated possibility of operation that does not have swinging signal and AGC (automatic gain control) 3 when this district carries out replay operations.Therefore, when PID carried out replay operations, the switch 505 among the AGC of Fig. 5 (automatic gain control) 1 to 3 disconnected, and keeps AGC (automatic gain control) operation, so that prevent saturated.Incidentally, because the swing of plane and groove exists synchronously between the groove of PID district and dish, so detect after first PID district, count the position of detecting this PID by microcomputer to swinging signal or from the clock signal of oscillating signal playback, and keep AGC (automatic gain control) operation.Like this, might prevent that the AGC (automatic gain control) because of there not being swinging signal to cause in the PID district is saturated.
By aforesaid operations, in the circuit of Fig. 1 and Fig. 5, might be at record and operation A GC (automatic gain control) circuit stably when playback CD-R/RW, DVD-R/RW and DVD-RAM.
Fig. 7 illustrates the example of the circuit structure of BPF circuit 23.Label 601,602 and 607 expression operational amplifiers, and operational amplifier 602 has constituted Switch Type Capacitor Filter with switch 603 and electric capacity 604 to 606 by clock signal control.Similarly, operational amplifier 607, switch 608 and electric capacity 609 to 611 have constituted Switch Type Capacitor Filter, and operational amplifier 601 and two-stage Switch Type Capacitor Filter have constituted the statevariable type wave filter.The passband of this wave filter is determined by the cutoff frequency fc of Switch Type Capacitor Filter.When the capacitance of electric capacity 604 is that the capacitance of C1, electric capacity 606 is C2 and switching frequency when being fsw, the fc of the Switch Type Capacitor Filter that operational amplifier 602 constitutes is expressed from the next.
fc=(1/2π)X(C1/C2)×fsw
Because the fc of wave filter is directly proportional with switching frequency, thus when since playback speed change and to cause that hunting frequency changes and when the clock frequency that swing is reset changes, the fc of Switch Type Capacitor Filter also corresponding change with being directly proportional.Like this, the passband of BPF is directly proportional with hunting frequency, and need not to finish the passband setting of BPF, thereby can reduce loaded down with trivial details processing by means such as the register such as outside microcomputer are provided with.Moreover the signal to noise ratio (S/N ratio) that might reduce the swinging signal that passband setting and the deviation between the swinging signal frequency because of BPF cause descends, and reduces the increase of the shake of the clock that produces from swinging signal.
The ratio of hunting frequency and clock frequency is 1: 186 among DVD-R/RW and the DVD-RAM, and this is different from 1: 196 hunting frequency and the ratio of clock frequency among the CD-R/RW.Handle this species diversity by following mode: the control signal 102 change switches 612 and 613 by Fig. 7 change capacitance C1, so that change the scale-up factor between fc and the fsx.Structure in view of the above by the BPF of Fig. 1 and Fig. 7, might be handled the high-speed record, high-speed replay of CD-R/RW, DVD-R/RW and DVD-RAM, such as variable record and the variable playback of CAV.
Incidentally, under situation because of the swinging signals of can not resetting such as cut, finger mark of dish, since the clock of not resetting, the instability so the passband of wave filter becomes.Therefore, the flaw indication that defect detection circuit obtains comes gauge tap 615 and 616 as BPF holding signal 617, and these switches are connected with resistance terminal when detecting defective, so that the passband of wave filter is fixed.
Equally, circuit structure according to first embodiment, oscillating signal playback circuit can handle the high-speed record, high-speed replay of CD-R/RW, DVD-R/RW and DVD-RAM, such as the variable record of CAV and the variable playback stable swinging signal of resetting, and the circuit erection space on the disc reproducing apparatus can be reduced widely.
Next second embodiment of the present invention will be described.Fig. 8 is the block scheme of present embodiment.In this accompanying drawing, have with the unit of the unit identical function of Fig. 1 use with Fig. 1 in identical character representation, and its explanation is omitted.Label 28 expression broadband subtraction circuits, the output signal that output signal deducts BPF 23 is recommended in the broadband that it obtains with subtraction circuit 117.Like this, can from the LPP output of Fig. 1, eliminate the hunting frequency component, might realize that more stable LPP detects.
Fig. 9 illustrates the example of AGC in the present embodiment (automatic gain control) circuit structure.In this accompanying drawing, have with Fig. 5 in the unit of AGC (automatic gain control circuit) identical function with identical character representation, and its explanation is omitted.Label 801 expression electric capacity switches, it changes electric capacity 506 and 802 by control signal 101.Capacitance C0 and C1 set according to following relation in this accompanying drawing.
C1>>CO
The AGC of present embodiment (automatic gain control) operation will be illustrated hereinafter.
When playback CD-R/RW, because RF signal and swinging signal are reset with being stabilized, there are not situations such as seepage, interruption, so switch 801 is selected the electric capacity 506 of little capacitance and do not changed.
When playback of DVD-R/RW, as shown in Figure 6, owing to the LPP RF signal that bleeds exists amplitude to change, so switch 801 is selected the electric capacity 802 of big capacitance when playback LPP.Like this, it is big that AGC (automatic gain control) response time constant becomes, thereby respond slack-off.Therefore, AGC (automatic gain control) does not follow the wobble amplitude that the seepage owing to LPP causes and changes and the variation of RF amplitude, and is the same with embodiment 1, so can obtain the effect of stable oscillation amplitude.The same with embodiment 1, by by microcomputer to count the detection of carrying out LPP from the clock signal of oscillating signal playback.
When playback of DVD-RAM owing to do not have signal at PID district AGC (automatic gain control) input end, so when playback PD district switch 801, the response time constant change of AGC (automatic gain control) circuit is greatly.The same with embodiment 1, by by microcomputer to count the detection of carrying out PD from the clock signal of oscillating signal playback.Like this, prevented because of AGC (automatic gain control) faulty operation due to the input end no signal, in addition by the PID district time also operation A GC (automatic gain control) stably.
From the above mentioned, the same with embodiment 1 in the present embodiment, can be at record and operation A GC (automatic gain control) stably when playback CD-R/RW, DVD-R/RW and DVD-RAM, and the identical effect of acquisition and embodiment 1.
Figure 10 illustrates the example of BPF circuit structure in the present embodiment.Label 901 and 902 expression gm variable amplifiers, gm (output current is to the mutual conductance of input voltage) changes with the current value of current source 905 basically with being directly proportional.This circuit constitutes two No. four wave filters by amplifier 901,902 and electric capacity 903,904.Have a kind of like this structure that output current value substantially is directly proportional with input clock frequency by the current source 905 that is used in control gm, the same with the BPF circuit of embodiment 1, can be substantially and the passband that is varied to direct ratio ground change BPF of playback speed.
Moreover, as shown in figure 11, according to control signal 102, by the scale-up factor between clock frequency and the output current in the change current source 905, might handle the dish of ratio with different hunting frequencies and clock frequency, such as CD-R/RW, DVD-R/RW and DVD-RAM etc., and can obtain the effect identical with the BPF circuit of embodiment 1.Incidentally, the flaw indication that defect detection circuit obtains comes gauge tap 907 as holding signal 617, and switch 907 is connected with the current source of fixing when detecting defective.Like this, there is not swinging signal not reset under the situation of clock at cut, finger mark etc. because of dish, the fixing passband of BPF, and can stably operate this wave filter.
Adopt this AGC (automatic gain control) circuit and BPF circuit structure, even in embodiment 2, also can obtain the effect identical with embodiment 1.
Figure 12 is the circuit block diagram of third embodiment of the invention.In this accompanying drawing, have with Fig. 1 in the unit of unit identical function use with Fig. 1 in identical character representation, and its explanation is omitted.Label 101 expression in this accompanying drawing is used for the control signal that keeps the operation of AGC (automatic gain control) circuit or be used to change the response time constant of embodiment 1 and embodiment 2, the defect detection signal 618 of this control signal and the cut of exporting from defect detection circuit 1102, finger mark etc. is input to or circuit 1 104, to produce AGC (automatic gain control) control signal 1105.Like this, not only for the LPP district of DVD-R/RW and the PID district of DVD-RAM, and, can make AGC (automatic gain control) stable operation, and can improve the reliability of swinging signal for defective such as the cut etc. of dish.
In addition, monitor from the frequency of the clock signal of oscillating signal playback by microcomputer, under the situation that frequency change is big when normal playback, output BRF holding signal 617.Like this, under the swinging signal of not resetting because of cut, finger mark etc. is not reset the situation of clock, fixing BPF passband, and can stably operate this wave filter.
As mentioned above, in the present embodiment, make the push-pull signal testing circuit have the broadband, and when playback of DVD-R/RW, the push-pull signal of output is inputed to the LPP testing circuit and detect LPP.Like this, can detect the LPP signal by oscillating signal playback circuit, and can reduce circuit scale.
In addition, also has a kind of function, can be kept for accurately eliminating the operation of AGC (automatic gain control) circuit of level behind AGC (automatic gain control) circuit of RF signal and the BPF by control signal from microcomputer, perhaps can switching time constant.Like this, AGC (automatic gain control) variation that the RF signal causes because the LPP signal bleeds in the LPP district in the time of might restraining playback of DVD-R/RW.In addition, in the time of might preventing playback of DVD-RAM in the ID district because the faulty operation that swinging signal disappears and causes such as AGC (automatic gain control) the saturated grade of output signal.
In addition, adopt this spline structure: the BPF passband clock frequency basic and from the swing playback that is used to extract hunting frequency is directly proportional, and the scale-up factor of clock frequency and BPF passband can be changed.Like this, for the dish of ratio,, can utilize identical BPF to extract hunting frequency such as CD-R/RW, DVD-R/RW and DVD-RAM etc. with different hunting frequencies and clock frequency.
Incidentally, the circuit structure of explanation is as just example in the embodiment of the invention 1 to embodiment 3, and AGC (automatic gain control) circuit and BPF circuit are not limited to embodiments of the invention.In addition, LPP testing circuit structure, keep AGC (automatic gain control) circuit and switching time constant the method and the fixing method of BPF passband, their combination also is not limited to embodiments of the invention.
As mentioned above, for recordable and CD that can reset, such as CD-R/RW, DVDR/RW and DVD-RAM, oscillating signal playback circuit swinging signal of can stably resetting in addition, by this circuit, can also be carried out LPP to DVD-R/RW and detect.Like this, can reduce the circuit erection space of disc reproducing apparatus widely.